1. Field of the Invention
The present invention relates to methods for manufacturing piezoelectric elements.
2. Related Background Art
Known piezoelectric elements include piezoelectric elements having a structure wherein an epitaxially grown lead zirconate titanate (PZT) layer is sandwiched between a pair of metallic layers. In the manufacture of such a piezoelectric element, the metallic layer and the PZT layer are sequentially epitaxially grown on a substrate, and then the PZT layer is processed. Ordinary methods for processing the PZT layer include wet etching using an etching solution (for instance, Japanese Patent Application Laid-open No. 2004-31521, Japanese Patent Application Laid-open No. 2001-116943, and U.S. Pat. No. 4,759,823).
Japanese Patent Application Laid-open No. 2004-31521 discloses a method for processing PZT layers using an etching solution that contains any acid from among hydrogen fluoride (HF), buffered hydrofluoric acid (BHF), diluted hydrofluoric acid (DHF), sulfuric acid (H2SO4), hydrochloric acid (HCl) or nitric acid (HNO3). Japanese Patent Application Laid-open No. 2001-116943 discloses a method for processing amorphous PZT layers using a 12% aqueous solution of HCl as an etching solution. U.S. Pat. No. 4,759,823 discloses a method for processing PZT layers formed by a sol-gel method, by employing an etching solution that contains HCl, HF and ammonium fluoride (NH4F) in weight concentrations of 0.35 wt % to 35 wt %, 0.01 wt % to 2.2 wt %, and 0.02 wt % to 9.3 wt %, respectively, relative to the weight of the etching solution.
When using an etching solution such as the above-described ones, containing an acid such as hydrochloric acid, for processing epitaxially grown PZT layers, the etching rate of the PZT layer by the etching solution was either very high or very low, and hence it was difficult to process PZT layers at an appropriate etching rate. Pattern shapes are difficult to control when the etching rate is very high. The pattern edge shape becomes unstable as a result. On the other hand, a very low etching rate entails lower productivity.